When to spray/mist duck eggs

I have 21 duck eggs in the incubator at school. I know there is at least 1 that is alive that I checked this morning - need to check the rest, they just don't look like the images on the metzer farm candling pictures.
But regardless, there is at least 1 alive - when do I mist them in the incubator?
There are also 4 bantam chicken eggs in there - should I be misting them too?